Autoreactive T cells recognizing myelin basic protein (MBP) and proteolipid apoprotein (PLP) are found in normal individuals and patients with MS. Thus we postulate that the inappropriate activation of MBP, PLP or perhaps other autoreactive T cells mediates the initial inflammatory insult leading to the recruitment of effector inflammatory cells in MS. The central theme of this revised grant is to examine the hypothesis that the key immunologic event in MS is the activation and change in effector function of T cells specific for CNS myelin antigens. During the last grant period, we provided evidence to suggest that autoreactive T cells in MS patients are functionally different compared to controls. We will now determine the nature of this difference by examining the following major functional consequences of T cell activation: the state of T cell activation (i.e. naive or differentiated) by examining whether MBP reactive T cells in MS patients are in the pool of differentiated T cells expressing CD45RO as compared to controls (aim 1.1); whether there are different patterns of cytokine usage of autoreactive T cells in MS patients as compared to controls (aim 1.2); and lastly, whether MBP reactive T cells from MS patients as compared to controls are resistant to tolerance induciton using CPS cells that are co-transfected with DR2 and the recently described family of B7 co-stimulatory ligands, B7-1 or B7-2 as APC (aim 1.3). The regulation of these activated, potentially pathogenic myelin reactive cells via T-T cell interactions will be examined in aim 2, and lastly, the identification of tolerogenic MBP epitopes as a prelude for designing peptide analogs to induce T cell tolerance and to examine signaling events that may down regulate activated, autoreactive T cells will be examined in aim 3. These last studies require an understanding of the TCR recognition of peptide/MHC complex. Investigations of T cell cytokine profile and function of myelin reactive T cells in MS may give insight into the pathogenesis of the disease and other autoimmune disorders. Perhaps of greater importance, aim two provides the basis for identifying the regulation of myelin reactive T cells while aim three allows the possible design of tolerogenic MBP epitopes as a prelude the designing peptide analogs for T cell tolerance induction. Understanding the nature of the effector cells in MS patients is critical for the development of novel immunotherapeutic strategies, which is the direct goal of these studies.